Composition and method for hydraulic fracturing and evaluation and diagnostics of hydraulic fractures using infused porous ceramic proppant

ABSTRACT

A composition and method for hydraulically fracturing an oil or gas well to improve the production rates and ultimate recovery using a porous ceramic proppant infused with a chemical treatment agent is provided. The chemical treatment agent may be a tracer material that provides diagnostic information about the production performance of a hydraulic fracture stimulation by the use of distinguishable both water soluble and hydrocarbon soluble tracers. The tracer can be a biological marker, such as DNA. The porous ceramic proppant can be coated with a polymer which provides for controlled release of the chemical treatment agent into a fracture or well bore area over a period of time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application that claims priority toU.S. patent application Ser. No. 14/213,276, filed Mar. 14, 2014, whichclaims priority to and the benefit of U.S. Provisional PatentApplication No. 61/929,761, filed Jan. 21, 2014. U.S. patent applicationSer. No. 14/213,276, filed Mar. 14, 2014, claims priority to and thebenefit of U.S. Provisional Patent Application No. 61/914,441, filedDec. 11, 2013. U.S. patent application Ser. No. 14/213,276, filed Mar.14, 2014, claims priority to and the benefit of U.S. Provisional PatentApplication No. 61/885,334, filed Oct. 1, 2013. U.S. patent applicationSer. No. 14/213,276, filed Mar. 14, 2014, claims priority to and thebenefit of U.S. Provisional Patent Application No. 61/883,788, filedSep. 27, 2013. U.S. patent application Ser. No. 14/213,276, filed Mar.14, 2014, claims priority to and the benefit of U.S. Provisional PatentApplication No. 61/803,652, filed Mar. 20, 2013. U.S. patent applicationSer. No. 14/213,276, filed Mar. 14, 2014, claims priority to and thebenefit of U.S. Provisional Patent Application No. 61/787,724, filedMar. 15, 2013. The above referenced patent applications are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to methods for hydraulically fracturing anoil or gas well to improve the production rates and ultimate recoverywith porous ceramic proppant infused with a chemical treatment agent.

The present invention also relates to methods for evaluating theeffectiveness and performance of a hydraulic fracturing stimulationtreatment in an oil or gas well with porous ceramic proppant infusedwith a biological marker.

BACKGROUND

In order to stimulate and more effectively produce hydrocarbons from oiland gas bearing formations, and especially formations with low porosityand/or low permeability, induced fracturing (called “frac operations”,“hydraulic fracturing”, or simply “fracing”) of the hydrocarbon-bearingformations has been a commonly used technique. In a typical hydraulicfracturing operation, fluid slurries are pumped downhole under highpressure, causing the formations to fracture around the borehole,creating high permeability conduits that promote the flow of thehydrocarbons into the borehole. These frac operations can be conductedin vertical, horizontal or deviated boreholes, and in either intervalsof uncased wells, or in cased wells through perforations.

In cased boreholes in vertical wells, for example, the high pressurefluids exit the borehole via perforations through the casing andsurrounding cement, and cause the oil and gas formations to fracture,usually in thin, generally vertical sheet-like fractures in the deeperformations in which oil and gas are commonly found. These inducedfractures generally extend laterally a considerable distance out fromthe wellbore into the surrounding formations, and extend verticallyuntil the fracture reaches a formation that is not easily fracturedabove and/or below the desired frac interval. The directions of maximumand minimum horizontal stress within the formation determine theazimuthal orientation of the induced fractures.

The high pressure frac fluids typically contain particulate materialscalled proppant. Proppant is generally composed of sand, resin-coatedsand or ceramic particles, and the fluid used to pump the proppantdownhole is typically designed to be sufficiently viscous to assist inentraining the proppant particles in the fluid as it moves downhole andout into the induced fractures.

After the proppant has been placed in the fracture and the fluidpressure relaxed, the fracture is prevented from completely closing bythe presence of the proppants which thus provide a high conductivityflow path to the wellbore which results in improved productionperformance from the stimulated well.

When the fracture closes, a compressive “closure” stress (oftenexceeding 10,000 psi) is placed on the proppant. At closures stressesexceeding about 5,000 psi, sand and resin-coated sand proppants losemuch of their ability to provide a conductive conduit in the fracturefor formation fluids. The sand grains fail or are crushed under thesestresses resulting in the generation of fines and a consequent reductionof porosity and permeability within the fracture. Resin-coating of thesand can reduce the generation of fines and extend the utility of sandsto some degree. Ceramic proppants are much stronger than sands andresin-coated sands, however, and can provide much greater conductivityin the fracture at all closure stresses. Consequently, ceramic proppantsare often used to provide much greater conductivity in the createdfracture to improve the production rates and hydrocarbon recoveries.

Ceramic proppants may be manufactured from a variety of starting rawmaterials which, along with the manufacturing process employed, willdefine the performance characteristics of the proppant. FIG. 1 showscomparisons of the permeability of three types of common ceramicproppants: a lightweight proppant, an intermediate density proppant anda high density proppant. These proppants differ primarily due to thecomposition of the starting raw materials from which they are made. Inthe case of lightweight ceramic proppant, the starting raw material istypically kaolin clay containing approximately 50% alumina oxide(Al₂O₃). The starting raw material for an intermediate density ceramicproppant is typically a bauxitic clay containing about 75% alumina oxideand the starting raw material for a high density ceramic proppant isalso typically a bauxitic clay but with an alumina oxide content ofabout 85%. The differences in alumina content of the starting rawmaterials lead to differences in the final crystalline structure of thesintered ceramic proppant and thus differences in the mechanicalproperties of the three types of ceramic proppants. These comparisonsassume somewhat similar processing characteristics. Proppant of similaralumina content may vary in performance due to variability in thequality of the processing. Further, a combination of higher aluminacontent with improved processing may lead to even higher conductivities.

For many oil and gas wells the composition of the fluids produced whichinclude hydrocarbons, hydraulic fracturing fluids, and formation watersis such that it is beneficial to add to the fluids a chemical treatmentagent to inhibit deleterious properties which the fluids might otherwiseexhibit.

Typical chemical treatment agents provide some function that is usefulfor the production performance of a hydraulically fractured well. Forexample, the produced fluids may be corrosive to the well casing so acorrosion inhibitor may be added to the fracturing fluid or subsequentlypumped into the producing formation in a “squeeze operation”. In anotherexample, paraffin or wax control is desirable to control the depositionof higher molecular weight hydrocarbons in an oil and gas stream.

The deposition of paraffin or wax inhibits flow, and if it occursdownhole can reduce well production by “choking off” the well in thearea of deposition. The effectiveness of wax inhibitors is generallymeasured using techniques that report pour point or pour pointdepression, which is the temperature at which a particular crude oilsample is “pourable” by standard measurement techniques. Anothercommonly used test method is the “wax appearance temperature” which usesan optical technique to determine the temperature at which wax or waxcrystals first appear. By either of these test methods, a lowering ofthe measured temperature is the objective of the paraffin or waxinhibitor. Paraffin inhibitors are typically classified by function.Those inhibitors that affect the wax appearance temperature are usuallyreferred to as wax inhibitors or wax crystal modifiers. Those inhibitorsthat affect the pour point are referred to as pour point depressors(PPD) or flow improvers. There is significant overlap in the structureand function of these two types of inhibitors and suitable inhibitorsgenerally include ethylene polymers and copolymers, combinationpolymers, and branched polymers with long alkyl chains.

Many other types of chemical treatment agents may also be used in theprevention of various deleterious reactions that may occur in oil andgas wells including scale inhibitors, hydrate inhibitors, asphalteneinhibitors and other organic deposition inhibitors, biocides,demulsifiers and other oilfield treatment chemicals.

One technique for delivering such chemical treatment agents downholeincludes infusing porous ceramic proppant particulates with the chemicaltreat agent. As described in U.S. Pat. Nos. 5,964,291 and 7,598,209, thefraction of chemically infused proppant added to standard proppant in ahydraulic fracturing operation is determined by the amount of thechemical treatment agent that is desired to be incorporated in thefracturing operation. This in turn is a function of the porosity of theporous ceramic proppant particulates and the degree to which thechemical treatment agent can be placed in the pore spaces of the porousceramic proppant particulates.

U.S. Pat. No. 5,964,291 discloses that porous ceramic proppants may besufficiently strong to be used on their own or in conjunction withparticles of non-porous materials. However the changes in conductivityof the propped fracture resulting from the use of the porous ceramicproppant as compared to standard proppant is not disclosed. It isfurther disclosed that the porous particles should comply with APIspecifications for crush resistance but again the relationship toconductivity impairment is not disclosed. No method for mitigatingconductivity impairment should it occur is disclosed.

U.S. Pat. No. 7,598,209 similarly discloses that porous proppants may besufficiently strong to be used on their own or in conjunction withparticles of non-porous materials again without disclosure of theeffects on conductivity. It is further disclosed that the porousparticulate may be any porous ceramic particulate that has requisitephysical properties such as desired strength to fit particular downholeconditions but no disclosure of what this means is offered. U.S. Pat.No. 7,598,209 offers one example of conductivity impairment in which theconductivity and permeability of a typical frac sand—a 20/40 meshOttawa—is compared to a 20/40 mesh Ottawa sand containing 10% of aceramic proppant with 12% porosity that has been chemically infused. Thedata presented show a conductivity reduction of 8%, 20% and 24% at 2 k,4 k and 6 k psi closure stress respectively when the porous ceramic isadded to the Ottawa sand.

In many instances, the chemical treatment agent must first be dissolvedin an aqueous, organic or inorganic solvent to enable the infusion ofthe chemical treatment agent into the porous ceramic proppantparticulates. If the chemical treatment agent is too viscous, however,this can result in lower effective amounts of the chemical treatmentagent being present in the infused proppant than desired or uneven orineffective infusion altogether. Dissolving the chemical treatment agentin the solvent is also an additional step that can be costly and timeconsuming. It would therefore be beneficial to infuse a chemicaltreatment agent directly into porous ceramic proppant particulateswithout the need for a solvent.

Tracers have been used in connection with hydraulic fracturing, toprovide certain types of diagnostic information about the location andorientation of the fracture. For example, U.S. Pat. Nos. 3,987,850 and3,796,883 describe the use of radio-active tracers to monitor thefunctioning of a well gravel pack. Tracers for hydraulic fracturing havebeen associated with various carrier materials as particles from whichthe tracer itself is released after placement in the created hydraulicfracture. U.S. Pat. No. 6,723,683 discloses starch particles as acarrier for a variety of oilfield chemicals including tracers. U.S.Patent Application Publication No. 2010/0307745 discloses the use oftracer particles in conjunction with hydraulic fracturing in which thetracer particles are composed of a tracer substance and a carrierwherein the carrier is comprised of starch or polymeric materials.

Carriers such as starch or polymeric materials are weak materials whichif added to standard proppant, and particularly a ceramic proppant, in ahydraulic fracture can negatively affect conductivity. Further, thedensities of starch or polymeric carrier materials are not similar toproppants typically used in hydraulic fracturing resulting in densitysegregation which can lead to non-uniform distribution of the tracerchemicals in the created fracture.

Tracers incorporated into hydraulic fracturing operations can provideinformation to operators which can enable them to improve completion andstimulation programs. This is accomplished by placing one or more uniquetracers in various portions of the fracturing operation, such as indifferent stages if multiple fracturing stages are performed in the wellor in different portions of a stage. Analysis of the produced fluids forthe presence of the tracers can provide diagnostic information as towhich stages or portions of a stage are in contact with the producedfluids. Tracers which differentially partition into the hydrocarbon orwater phases can provide further diagnostic data regarding the relativehydrocarbon to water ratio of the produced fluids from a stage.

Nanoparticle dispersions and surfactants have been used in connectionwith hydraulic fracturing to provide improved fluid production from awell. For example, U.S. Patent Publication No. 2010/0096139 describesthe use of a fluid mixture of nanoparticles and a wetting agent that isinjected or pumped into a well to enhance the wetting characteristics ofthe formation surfaces. Similarly, U.S. Pat. No. 7,380,606 describes theuse of a solvent-surfactant blend that is injected or pumped into asubterranean formation to improve fluid recovery.

The wetting characteristics, or wettability, of a solid surface isdefined as the preference of the solid surface to come into contact withthe wetting phase, i.e., a liquid, such as water or oil, or a gas.Wettability has an impact on qualities such as permeability andconductivity. For example, a water-wet formation or proppant surface—onethat exhibits a preference for coming into contact with water as opposedto a hydrocarbon—may lead to decreased hydrocarbon permeability andtherefore decreased hydrocarbon recovery. Other chemical treatmentagents such as surfactants and nanoparticle dispersions, however, may beintroduced into a fracture to alter the wetting characteristics of thefracture environment to improve the desired permeability and recovery.

For non-porous, solid surfaces such as a formation surface, the wettingphase will spread across the surface. For porous, solid surfaces, suchas porous ceramic proppant, the wetting phase may be absorbed by thesurface. Pumping fluids containing nanoparticle dispersions orsurfactants into a formation in liquid form may improve the wettabilityof a formation surface, but may not provide any significant or long-termimprovement in the wetting characteristics of the proppant, andtherefore would not offer the corresponding improvement in proppantconductivity that promotes hydrocarbon production, reservoir waterproduction, or frac fluid clean up or production.

In the case of a horizontal well, as many as 40 separate hydraulicfracturing operations, or stages, may be conducted. It may sometimes bedesirable to utilize unique tracers in each of these stages and furtherto determine the relative amounts of hydrocarbons and water productionfrom each of the stages. In addition, one may wish to determine therelative fluid production from different portions of each of the 40stages. It is also desirable for the tracers to be released over anextended period of time of perhaps months or years. In such a scenario,more than 100 unique tracers would be required. Further, to be costeffective the amount of each tracer required should ideally be limited.Tracers in the prior art are limited in number and could not accomplishthis task. Additionally, many of the prior art tracers cannotpreferentially partition into the hydrocarbon or water phases anddetection limits are too high for long term identification especiallywhen placed directly in the frac fluid.

Therefore, what is needed is a method to add porous chemically infusedceramic proppant to standard non-porous proppant in a manner that willnot negatively impair proppant conductivity. Also, what is needed is atracer carrier that does not segregate from the standard proppant whenadded in a hydraulic fracture and that does not negatively impactconductivity. Additionally, what is needed is a method of alteringwettability of a proppant through the infusion of nanoparticledispersions or surfactants into the porous proppant to increase fluidproduction.

Also, it would be beneficial to have a tracer technology that canprovide a very large number of unique tracers that are capable ofpartitioning into either of the hydrocarbon or water phases as desired,are detectable at very low concentrations in the produced fluids for anextended period of time, and are not subject to degradation at the hightemperatures and pressures often found in well formations.

Additionally, in many well operations, the release of the chemicaltreatment agent over an extended period of time is desirable. What isneeded is a porous ceramic proppant infused with a chemical treatmentagent and a method of introducing the proppant into a fracture such thatthe release of the chemical treatment agent into the fracture or wellarea can be controlled over an extended period of time. Also, what isneeded is a semi-permeable coating for the proppant that issubstantially non-degradable in the presence of the well fluids butpermits diffusion of the chemical treatment agent through thesemi-permeable coating so as to release the chemical treatment agentinto the fracture or well area over an extended period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may best be understood by referring to thefollowing description and accompanying drawings that are used toillustrate embodiments of the invention. In the drawings:

FIG. 1 is a graphical representation of a comparison of proppantpermeability for lightweight ceramic proppant, intermediate densityceramic proppant, and high density ceramic proppant.

FIG. 2 is a graphical representation of the long term permeability of astandard non-porous light weight ceramic proppant and a light weightporous ceramic proppant (at 25% porosity).

FIG. 3 is a graph of an elution profile for Example 1 in terms of DTPMP(diethylenetriamine penta(methylene phosphonic acid)) in parts permillion (ppm) released as a function of time for porous ceramic proppantinfused with DTPMP and encapsulated with various coatings.

FIG. 4 is a graph of the elution profile for Example 2 in terms of theppm of DTPMP released as a function of time for porous ceramic proppantinfused with DTPMP and encapsulated with various coatings.

FIG. 5 is a graph of the elution profile for Example 3 in terms of theppm of DTPMP released as a function of time for porous ceramic proppantinfused with DTPMP and encapsulated with various coatings.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knownstructures and techniques have not been shown or described in detail inorder not to obscure the understanding of this description.

The term “apparent specific gravity,” as used herein, is the weight perunit volume (grams per cubic centimeter) of the particles, including theinternal porosity. The apparent specific gravity values given hereinwere determined by the Archimedes method of liquid (water) displacementaccording to API RP60, a method which is well known to those of ordinaryskill in the art. For purposes of this disclosure, methods of testingthe characteristics of the proppant in terms of apparent specificgravity are the standard API tests that are routinely performed onproppant samples.

The term “conductivity,” as used herein, is defined as the product ofthe width of the created fracture and the permeability of the proppantthat remains in the fracture.

The term “high density proppant,” as used herein, means a proppanthaving an apparent specific gravity of greater than 3.4 g/cm³.

The term “intermediate density proppant,” as used herein, means aproppant having an apparent specific gravity of from about 3.1 to 3.4g/cm³.

The term “internal interconnected porosity,” as used herein, is definedas a percentage of the pore volume, or void volume space, over the totalvolume of a porous ceramic particulate.

The term “light weight proppant,” as used herein, means a proppanthaving an apparent specific gravity of less than 3.0 g/cm³.

The term “degradable,” as used herein, means the ability of a chemicalor coating to react to dissolve or breakdown into smaller componentsunder one or more downhole conditions.

According to certain embodiments of the present invention, a compositeceramic proppant composition for use in hydraulic fracturing isproduced. According to certain embodiments of the present invention, thecomposite ceramic proppant comprises a non-porous particulate part and aporous ceramic particulate part, wherein the porous ceramic particulateis infused with a chemical treatment agent. Furthermore, according tocertain embodiments of the present invention, the permeability andconductivity of the composite ceramic proppant composition is at leastequal to the permeability and conductivity of the non-porous particulatepart alone.

Ceramic proppants can be manufactured to a range of apparent specificgravity. For instance, U.S. Pat. No. 4,427,068, the entire disclosure ofwhich is incorporated herein by reference, discloses a method formanufacturing proppant with an apparent specific gravity of less than3.4 g/cm³. The method comprises preparing proppant pellets from a claymixture of at least 40% clay, and another material such as bauxite oralumina. The clay mixture comprises burley clay, flint clay and at least60% diaspore clay. The raw materials are blended in a mixer and water isadded until the composite forms spherical pellets. 5-15% of additionalceramic powder is then added to the pellets. The spherical pellets arethen dried and furnaced at sintering temperature until they reach anapparent specific gravity between about 2.7 and 3.4 g/cm³.

Also, U.S. Pat. No. 4,440,866, the entire disclosure of which isincorporated herein by reference, discloses a method for continuousprocess manufacture of proppant with an apparent specific gravity ofapproximately 3.7 g/cm³. The method comprises 1) preparing an aqueousfeed suspension of bauxite and a binder, 2) continuously atomizing thefeed suspension into a layer of already partly dried bauxite particlesfluidized in a stream of drying air, 3) continuously recoveringparticles from the layer, 4) continuously separating the particles intooversize, undersize, and product fractions, 5) continuously recyclingunsuitable material, and 6) drying and sintering the non-recycledproduct by heating at a temperature of between about 1200 and 1650° C.

In addition, U.S. Pat. No. 4,522,731, the entire disclosure of which isincorporated herein by reference, refers to the method disclosed in U.S.Pat. No. 4,440,866 to manufacture proppant having an apparent specificgravity of less than 3.0 g/cm³.

Moreover, U.S. Pat. No. 4,623,630, the entire disclosure of which isincorporated herein by reference, discloses a method for manufacturingproppant with an apparent specific gravity of between about 2.6 to 3.3g/cm³. The method comprises preparing proppant pellets from a mixture ofdried but uncalcined or partially calcined clays and bauxites and dustcollector fines with fully calcined materials. The raw materials areblended in a mixer and water is added until the composite formsspherical pellets. 5-15% of additional ceramic powder is then added tothe pellets. The spherical pellets are then dried and furnaced atsintering temperature until they reach an apparent specific gravitybetween about 2.6 and 3.3 g/cm³.

Further, U.S. Pat. No. 4,658,899, the entire disclosure of which isincorporated herein by reference, discloses a method for manufacturingproppant with an apparent specific gravity of between about 2.9 and 3.2g/cm³. The method comprises preparing proppant pellets from a mixture of40-70% dried but uncalcined clay, and bauxites and dust collector fineswith fully calcined materials. The raw materials are blended in a mixerand water is added until the composite forms spherical pellets. 5-15% ofadditional ceramic powder is then added to the pellets. The sphericalpellets are then dried and furnaced at sintering temperature until theyreach an apparent specific gravity between about 2.9 to 3.2 g/cm³.

Still further, U.S. Pat. No. 7,036,591, the entire disclosure of whichis incorporated herein by reference, discloses that ceramic proppantscan be manufactured to a range of apparent specific gravity. The rangeof apparent specific gravities reflects the range of internal porositypresent in the ceramic pellets.

According to certain embodiments of the present invention, the proppantcomposition has an apparent specific gravity of less than 3.1 g/cm³,less than 3.0 g/cm³, less than 2.8 g/cm³, or less than 2.5 g/cm³. Inother embodiments, the proppant composition has an apparent specificgravity of from about 3.1 to 3.4 g/cm³. In still other embodiments, theproppant composition has an apparent specific gravity of greater than3.4 g/cm³, greater than 3.6 g/cm³, greater than 4.0 g/cm³, or greaterthan 4.5 g/cm³.

According to several exemplary embodiments, the proppant compositionincludes a non-porous proppant. Suitable materials for use as thenon-porous particulate include lightweight non-porous ceramic proppant,intermediate density non-porous ceramic proppant and high densitynon-porous ceramic proppant.

According to several exemplary embodiments, the proppant compositionincludes a porous ceramic proppant. Suitable proppant materials for useas the porous ceramic proppant include lightweight porous ceramicproppant, intermediate density porous ceramic proppant and high densityporous ceramic proppant. U.S. Pat. No. 7,036,591, the entire disclosureof which is incorporated herein by reference, is directed to a proppanthaving a range of apparent specific gravity.

FIG. 1 is a graphical comparison of the permeability of light weightceramic proppant, intermediate density ceramic proppant, and highdensity ceramic proppant. As shown in FIG. 1, a high density ceramicproppant has a higher permeability than an intermediate density ceramicproppant which in turn has a higher permeability than a light weightceramic proppant. This variability results from the crystallinestructure differences arising from the difference in composition of thestarting raw materials. FIG. 2 is a graphical representation of the longterm permeability of a standard non-porous light weight ceramic proppantand a light weight porous ceramic proppant (at 25% porosity). Standardceramic proppants are generally manufactured so as to eliminate as muchporosity as is practically possible in the individual particulates inorder to maximize the inherent strength of the particles. This isconsistent with the nature of ceramic bodies in that they tend to failas a function of the size of the largest internal flaw and in thiscontext an internal open pore space is a flaw. Consequently, in ageneral sense, the lower the internal porosity with small pore sizes,the stronger the ceramic body. Conversely, in a general sense, thegreater the overall amount of internal porosity and large pore size of aceramic particulate the weaker will be its inherent strength. Thus, theconductivity of a light weight ceramic proppant in which there is 10%porosity in the particle will be lower than the conductivity of alightweight ceramic proppant having 5% porosity which in turn will belower than a non-porous light weight ceramic proppant.

Further, the comparison shown in FIG. 1 for non-porous ceramicparticulates can be duplicated for porous ceramic particulates.Specifically, a high density porous ceramic proppant that has a porosityof the particulate of 12% will have a higher permeability than anintermediate density ceramic proppant with 12% particulate porosity,which in turn will have a higher permeability than a light weightceramic proppant with 12% particulate porosity.

According to several exemplary embodiments of the present invention, theporous ceramic particulates are infused with one or more chemicaltreatment agents. Methods for infusing porous ceramic particulates withchemical treatment agents are well known to those of ordinary skill inthe art, such as those disclosed in U.S. Pat. Nos. 5,964,291 and7,598,209, the entire disclosures of which are incorporated herein byreference. According to several exemplary embodiments, the porousceramic particulates act as a carrier for the chemical treatment agentin a hydraulic fracturing operation.

According to several exemplary embodiments of the present invention, inorder to add porous, chemically infused ceramic proppant to standardnon-porous ceramic proppant in a hydraulic fracture in a way that doesnot impair the permeability or conductivity of the standard non-porousceramic proppant alone, requires the use of a combination of differenttypes of ceramic proppants for the standard non-porous and porousportions of the total ceramic proppant mass utilized in the fracturingoperation. For instance, according to several exemplary embodiments ofthe present invention, if the standard non-porous particulate selectedis a light weight ceramic proppant, the porous ceramic particulate canbe either an intermediate density ceramic proppant or a high densityceramic proppant. Also, according to several exemplary embodiments ofthe present invention, if the standard non-porous particulate selectedis an intermediate density proppant, the porous ceramic particulate canbe a high density ceramic proppant.

For example, the fraction of intermediate density porous ceramicproppant to be added to a standard non-porous light weight ceramicproppant will dictate the maximum porosity that the intermediate densityporous ceramic may have and not negatively impact permeability. In thisexample, if a 10% fraction of intermediate density porous proppant is tobe added to a standard light weight ceramic proppant then the maximumporosity of the intermediate density porous proppant may be 12% in orderto not reduce the permeability of the proppant as compared to thepermeability of the standard light weight ceramic proppant alone whereasadding a 10% fraction of an intermediate density porous proppant having20% porosity may be detrimental to proppant permeability.

According to several exemplary embodiments of the present invention, theporous, chemically infused porous ceramic proppant may have a similaralumina content as the standard non-porous ceramic proppant and can beadded to the standard non-porous ceramic proppant in a hydraulicfracture in a way that does not impair the permeability or conductivityof the standard non-porous ceramic proppant alone. According to suchembodiments, the porous and non-porous proppants are processed indifferent ways such that the mechanical properties of the chemicallyinfused porous ceramic proppant is approximately the same as or betterthat the mechanical properties of the standard non-porous ceramicproppant.

A ceramic proppant composition containing a mixture of porous ceramicproppant and non-porous ceramic proppant can have a conductivity that isat least about 10%, at least about 20%, at least about 30%, at leastabout 40%, at least about 50%, at least about 60%, at least about 70%,at least about 80%, at least about 90%, at least about 95%, or at leastabout 99% of the conductivity of the non-porous ceramic proppant. Forexample, the ceramic proppant composition containing a mixture of porousceramic proppant and non-porous ceramic proppant can have a conductivityfrom about 25% to about 125%, about 55% to about 115%, about 65% toabout 112%, about 75% to about 108%, about 85% to about 105%, about 95%to about 105%, or about 99.99% to about 102% of the conductivity of thenon-porous ceramic proppant.

According to several exemplary embodiments, a method of diagnosticevaluation of a hydraulic fracturing operation is provided, the methodcomprising: 1) injecting a hydraulic fluid into the subterraneanformation at a rate and pressure sufficient to open a fracture therein,and 2) injecting a proppant composition into the subterranean formation,wherein the proppant composition includes porous ceramic proppantinfused with a chemical treatment agent, 3) wherein the chemicaltreatment agent separates from the porous ceramic proppant over anextended period of time, 4) wherein the chemical treatment agent returnsto the surface with the produced fluids, and 5) wherein the chemicaltreatment agent is recovered and identified. According to severalexemplary embodiments, the chemical treatment agent is a biologicalmarker, or biological tag.

As noted above, ceramic proppants can be manufactured to a range ofapparent specific gravities and such range of specific gravitiesreflects the range of internal porosity present in the ceramic pellets.Typically, the internal porosity of commercial ceramic proppant is low(generally less than 5% and this internal porosity is notinterconnected). As disclosed in U.S. Pat. No. 7,036,591, however, theprocessing of ceramic proppants can be altered to generate within theindividual ceramic pellet a porosity exceeding 30%. As pellet porosityexceeds about 5%, the porosity of the pellet becomes interconnected.According to several exemplary embodiments, the internal interconnectedporosity in the porous ceramic proppant can be infused with a chemicaltreatment agent. Methods for infusing a porous ceramic proppants arewell known to those of ordinary skill in the art, for instance see U.S.Pat. Nos. 5,964,291 and 7,598,209, and similar processes such as vacuuminfusion, thermal infusion, capillary action, ribbon blending at room orelevated temperature, microwave blending or pug mill processing can beutilized to infuse porous ceramic proppants with chemical treatmentagents according to several exemplary embodiments of the presentinvention. Specifically, according to several exemplary embodiments,chemical treatment agents include tracers, scale inhibitors, hydrateinhibitors, hydrogen sulfide scavenging materials, corrosion inhibitors,paraffin or wax inhibitors, including ethylene vinyl acetate copolymers,asphaltene inhibitors, organic deposition inhibitors, biocides,demulsifiers, defoamers, gel breakers, salt inhibitors, oxygenscavengers, iron sulfide scavengers, iron scavengers, clay stabilizers,enzymes, biological agents, flocculants, naphthenate inhibitors,carboxylate inhibitors, nanoparticle dispersions, surfactants,combinations thereof, or any other oilfield chemical that may be deemedhelpful in the hydraulic fracturing process.

As noted above, the internal porosity in porous ceramic pellets can beinfused with a chemical treatment agent such as a tracer material sothat the porous ceramic pellets act as a carrier for the tracer in ahydraulic fracturing operation. By tailoring the type of porous ceramicpellets used as a carrier, according to the methods discussed above, anypotential impact to proppant conductivity by using the porous ceramicpellets can be avoided. According to certain embodiments of the presentinvention, the tracer material includes metallic or non-metallicnano-particles while in other embodiments, the tracer material includesa chemical tracer.

According to several exemplary embodiments, chemical tracer materials,such as the biological tags described in International PatentPublication No. WO2007/132137, are infused into porous ceramicparticulates. Generally, materials that may be used as chemical tracersinclude various dyes, fluorescent materials, as well as biologicalmarkers, such as DNA. Other chemical tracers include fluorinesubstituted compounds. According to several exemplary embodiments, inorder to ensure the tracer is reliably carried to the surface inproduced fluid, the tracer is soluble in the produced fluid. Theproduced fluid may be water or hydrocarbon and there are availabletracers that are only soluble in water or only soluble in liquidhydrocarbon or only soluble in hydrocarbon gases. This variablesolubility allows for more definitive diagnostic capabilities. Forexample hydraulic fracturing is often performed in stages. That is, theentire hydrocarbon bearing interval to be hydraulically fractured is notstimulated at one time but rather in stages. In the case of a horizontalwell, as many as forty separate hydraulic fracturing operations, orstages, may be conducted in the horizontal section. Because each stageof hydraulic fracturing entails additional cost, it is of interest todetermine how many of the stages are contributing to production from thewell and further which contributing stages are producing hydrocarbonsand which are producing water. The use of distinctive tracer materialscan accomplish this objective. For example, if a well is hydraulicallyfractured in five stages and it is of diagnostic importance to determinewhich of the stages are producing liquid hydrocarbons and which of thestages are producing water, then there may be introduced into theproppant for stage 1 a fraction of a porous ceramic proppant that has aunique liquid hydrocarbon-soluble Tracer 1H infused into the pores ofthe ceramic pellets thereof. Also, there may be added to this stage, afraction of the proppant that is a porous ceramic and has infused intothe pores of the ceramic pellet a unique water-soluble Tracer 1W. Forthe second stage of the hydraulic fracturing operation, then there maybe introduced into the proppant for stage 2 a fraction of a porousceramic proppant that has a unique liquid hydrocarbon soluble Tracer 2Hinfused into the pores of the ceramic pellets thereof. Also, there maybe added to this stage a fraction of the proppant that is a porousceramic and has infused into the pores of the ceramic pellet a uniquewater-soluble Tracer 2W. This method of adding uniquely distinguishablehydrocarbon-soluble and water-soluble tracers in the porous ceramic maycontinue for all or a portion of the subsequent stages. When the well isthen placed on production following the completion of the hydraulicfracturing operations, samples of the produced water and hydrocarbonsare then captured at different points in time following the start ofproduction and analyzed for the presence of the unique tracer materials.By determining the presence and relative concentration of each of thetracer materials, diagnostic determinations can be made of effectivenessof the stimulation and the hydrocarbon content of the stimulatedformation. This diagnostic information can then be utilized to optimizesubsequent hydraulic fracturing operations in nearby wells.

According to several exemplary embodiments, a composite ceramic proppantcomposition for use in hydraulic fracturing is produced. According toseveral exemplary embodiments, the composite ceramic proppantcomposition includes porous ceramic particulates infused with a chemicaltreatment agent. Furthermore, according to several exemplaryembodiments, the infused porous ceramic particulates are encapsulatedwith a coating. The coating can be or include one or more organic orinorganic materials. For example, the coating can be or include apolymeric material. According to several exemplary embodiments, theporous ceramic particulates are infused with a water-soluble chemicaltreatment agent such as a scale inhibitor, a salt inhibitor, orcombinations or mixtures thereof, and are then coated with ahydrocarbon-soluble chemical treatment agent such as a paraffininhibitor. According to such embodiments, the infused coated porousceramic proppant is placed in a fracture in a subterranean formation andonce hydrocarbon production begins, the presence of the hydrocarbonscauses leaching, elution, diffusion, bleeding, discharging, desorbing,dissolving, draining, seeping, or leaking of the hydrocarbon-solublechemical treatment agent from the proppant. After a certain period oftime, when water production begins, then the infused water-solublechemical treatment agent begins to leach, elute, diffuse, bleed,discharge, desorb, dissolve, drain, seep, or leak from the proppant.

According to several exemplary embodiments, the porous ceramicparticulates infused with a chemical treatment agent are coated with apolymeric material that forms a semi-permeable polymeric coating that issubstantially non-degradable in the presence of the well fluids butpermits the chemical treatment agent to leach, elute, diffuse, bleed,discharge, desorb, dissolve, drain, seep, and leak through the polymericcoating so as to release the chemical treatment agent into the fractureor well area. The amount and molecular weight of the semi-permeablesubstantially non-degradable polymeric coating can be varied to providefor longer or shorter release times for tailored release of the chemicaltreatment agents.

According to several exemplary embodiments, the chemical treatment agentis released from the porous ceramic particulates for a period of up toabout one year, up to about five years, or up to about ten years afterthe porous ceramic particulates are placed in a fracture in asubterranean formation.

According to several exemplary embodiments, the porous ceramicparticulates are coated with a semi-permeable substantiallynon-degradable polymer such as phenol formaldehyde, polyurethane,cellulose ester, polyamides, vinyl esters, epoxies, or combinationsthereof.

According to several exemplary embodiments of the present invention, theproppant pellets which are infused with a chemical treatment agentfurther include a degradable coating. Specifically, as the coatingdegrades, the chemical treatment agent infused in the proppant pelletswill be released into the fracture. The amount and molecular weight ofthe degradable coating can be varied to provide for longer or shorterdegrade times and tailored release of the chemical treatment agent.

According to certain embodiments, the degradable coating may include oneor more of water-soluble polymers and cross-linkable water-solublepolymers. Suitable water-soluble polymers and cross-linkablewater-soluble polymers are disclosed in U.S. Pat. No. 6,279,656, theentire disclosure of which is incorporated herein by reference.According to several exemplary embodiments in which the degradablecoating includes one or more of water-soluble polymers andcross-linkable water-soluble polymers, the solubility parameters of suchpolymers may be controlled to adjust the timing of the solubility ordegradation of the coating. Such parameters may include molecularweight, the hydrophilic/lipophilic balance of the polymers, and theextent of cross-linking of the polymers. According to several exemplaryembodiments, the degradable coating includes a degradable polymer suchas polylactic acid, cellulose acetate, methyl cellulose or combinationsthereof and will degrade inside the hydraulic fracture to allow for therelease of the infused chemical treatment agent at different timeintervals.

Also as noted above, the internal porosity in porous ceramic pellets canbe infused with a chemical treatment agent such as a nanoparticledispersion so that the porous ceramic pellets act as a carrier for thenanoparticle dispersion in a hydraulic fracturing operation. Theinfusion of the nanoparticle dispersion into the internal porosity ofthe porous ceramic proppant, rather than simply injecting or pumping thenanoparticle dispersion into a well formation in fluid form, improvesnot only the wetting characteristics of the formation surfaces but alsoof the proppant itself. The nanoparticle dispersion interacts with thesurface of the proppant to alter its wetting characteristics. Further,as fluids flow through the proppant pack in the formation, some of thenanoparticle dispersion may be released into the fracture and adhere toand improve the wettability of the formation surfaces. Thus, the use ofnanoparticle dispersions that are infused into proppant offers benefitssimilar to those obtained by pumping the nanoparticle dispersion intothe formation in fluid form, but the increased interaction of thenanoparticle dispersion with the proppant offers the additional benefitof improved wettability of the proppant.

Similarly, the internal porosity in porous ceramic pellets can beinfused with a chemical treatment agent such as a surfactant so that theporous ceramic pellets act as a carrier for the surfactant in ahydraulic fracturing operation. The use of a surfactant that is infusedinto the proppant itself, rather than simply pumped into a formation,also offers improved wetting characteristics of the proppant similar tothose described in conjunction with nanoparticle dispersions.

Nanoparticle dispersions may include a number of different nanoparticlematerials known to those of ordinary skill in the art, includingpolymers, silica, metals, metal oxides, and other inorganic materials,that are suspended in an aqueous or non-aqueous solvent fluid. Accordingto several exemplary embodiments, suitable materials include but are notlimited to nanoparticles such as silicon dioxide, zirconium dioxide,antimony dioxide, zinc oxide, titanium dioxide, aluminum dioxide,particles derived from natural minerals, synthetic particles, andcombinations thereof. According to several exemplary embodiments, one ormore of silicon dioxide, zirconium dioxide and antimony dioxide areadded at about 65 nanometers or less in diameter (in several exemplaryembodiments 1-10 nm) and have a polydispersity of less than about 20%.

The selection of a specific nanoparticle dispersion or surfactant to beinfused into the porous ceramic proppant depends on the necessaryadjustment in wetting characteristics of the proppant for the desiredproduction enhancement. Surfactants may be any selected from any numberof surfactants known to those of ordinary skill in the art, including,for example, anionic, cationic, nonionic, and amphoteric surfactants, orcombinations thereof. According to several exemplary embodiments,suitable surfactants include but are not limited to saturated orunsaturated long-chain fatty acids or acid salts, long-chain alcohols,polyalcohols, dimethylpolysiloxane and polyethylhydrosiloxane. Accordingto several exemplary embodiments, suitable surfactants include but arenot limited to linear and branched carboxylic acids and acid saltshaving from about 4 to about 30 carbon atoms, linear and branched alkylsulfonic acids and acid salts having from about 4 to about 30 carbonatoms, linear alkyl benzene sulfonate wherein the linear alkyl chainincludes from about 4 to about 30 carbon atoms, sulfosuccinates,phosphates, phosphonates, phospholipids, ethoxylated compounds,carboxylates, sulfonates and sulfates, polyglycol ethers, amines, saltsof acrylic acid, pyrophosphate and mixtures thereof. According toseveral exemplary embodiments, suitable surfactants include but are notlimited to sodium stearate, octadecanoic acid, hexadecyl sulfonate,lauryl sulfate, sodium oleate, ethoxylated nonyl phenol, sodium dodecylsulfate, sodium dodecylbenzene sulfonate, laurylamine hydrochloride,trimethyl dodecylammonium chloride, cetyl trimethyl ammonium chloride,polyoxyethylene alcohol, alkylphenolethoxylate, Polysorbate 80,propylene oxide modified polydimethylsiloxane, dodecyl betaine,lauramidopropyl betaine, cocamido-2-hydroxy-propyl sulfobetaine, alkylaryl sulfonate, fluorosurfactants and perfluoropolymers and terpolymers,castor bean adducts and combinations thereof. According to severalexemplary embodiments, the surfactant is sodium dodecylbenzene sulfonateor sodium dodecyl sulfate. According to several exemplary embodiments,the surfactants are used at a concentration below the critical micelleconcentration (CMC) in aqueous and hydrocarbon carrier fluids.

Suitable nanoparticle dispersions or surfactants may be selected fromany number of commercially available products. For example, nanoparticledispersion products are commercially available from FTS International®as NPD 2000® and NPD 3000®. Nanoparticle dispersions are alsocommercially available from CESI Chemical, Inc., a subsidiary of FlotekIndustries, Inc., as MA-844W, MA-845, StimOil® FBA M, StimOil® FBA Plus,and StimOil® FBA Plus Enviro. Further, surfactants as productionenhancement additives are commercially available from CESI Chemical,Inc., as SG-400N, SG-401N, and LST-36.

According to several exemplary embodiments of the present inventionwhich include a degradable coating on the proppant pellets, the chemicaltreatment agent includes metallic or non-metallic nanoparticles whichare added to the pore space of the porous proppant pellets and arereleased when the degradable coating dissolves in aqueous or hydrocarbonfluids. According to such embodiments, the nanoparticles flow to thesurface with the fluid and can be analyzed (chemically or otherwise) fortheir presence.

According to several exemplary embodiments of the present inventionwhich include a degradable coating on the proppant pellets, the chemicaltreatment agent infused into the proppant pellets includes nanoparticledispersions or surfactants which are added to the pore space of theporous proppant pellets and are released when the degradable coatingdissolves in aqueous or hydrocarbon fluids. According to suchembodiments, upon degradation of the coating, some of the nanoparticledispersions or surfactants are released upon exposure to passing fluids,and therefore improve the wettability of formation surfaces. The portionof the nanoparticle dispersions or surfactants remaining in the proppantwould improve the wettability of the proppant itself. According toseveral exemplary embodiments of the present invention, the degradablecoating would degrade inside the hydraulic fracture over a desiredperiod of time, thereby allowing for timed release of the chemicaltreatment agent and a longer effective life.

In an exemplary method of fracturing a subterranean formation, ahydraulic fluid is injected into the formation at a rate and pressuresufficient to open a fracture therein, and a fluid containing a proppantcomposition comprising a non-porous particulate and a porous ceramicparticulate infused with a chemical treatment agent, as described hereinand having one or more of the properties as described herein is injectedinto the fracture to prop the fracture in an open condition.

In several exemplary embodiments of the present invention, the internalinterconnected porosity of the porous ceramic proppant is in a rangefrom about 5-35%, or alternatively in a range from about 5-15%, or15-35%. As noted above, the internal interconnected porosity in porousceramic proppant can be infused with a chemical treatment agent such asa biological marker so that the porous ceramic proppant acts as acarrier for the biological marker in a hydraulic fracturing operation.According to several exemplary embodiments, the biological marker isDNA. DNA, or deoxyribose nucleic acid, is sometimes a double-strandedhelical molecule that encodes the genetic information of almost allliving systems. Each DNA molecule can be unique as a result of aparticular sequence of nitrogenous bases—adenine (“A”), thymine (“T”),cytosine (“C”) and guanine (“G”)—contained with the molecule. The doublehelix structure is formed and maintained by the pairing of a nitrogenousbase on one phosphate/sugar backbone carrier chain with a nitrogenousbase on the other phosphate/sugar backbone carrier chain throughhydrogen bonding. Specifically, an adenine base will pair with a thyminebase (an “AT” base pair), and a cytosine base will pair with a guaninebase (a “GC” base pair). Probability terms can be calculated for thefrequency of a given sequence of bases, and as long as a large enoughDNA molecule is used, the “uniqueness” of a particular molecule of DNAcan be known with sufficient certainty. The DNA molecule may benaturally occurring or a manufactured (synthetic) DNA and can be doublestranded or single stranded. Synthetic DNA is commercially available andmay be manufactured to order by several specialized DNA manufacturers,such as GenScript, Synthetic Genomics, DNA 2.0, Genewiz, Inc., LifeTechnologies, and Cambrian Genomics. Further, the DNA can be“encapsulated” to enhance its survivability at downhole reservoirconditions and to otherwise alter its interaction with formation fluids.Additionally, specific DNA sequences may be selected for use based oncompatibility with the thermal environment of a specific well.

Infusing the biological marker into the porous ceramic proppant ratherthan adding the biological marker directly to the fracture fluidspermits a long term diagnostic capability not otherwise available. Whenthe marker is added directly to the fracture fluid it will flow backimmediately with the fluid when the well is placed on production becausethere is no mechanism for the marker to remain in the well. Thus, thediagnostic benefits of adding the marker directly to the fracture fluidare limited. Conversely, when the biological marker is infused into aporous ceramic proppant, the elution of the marker is slow and can becontrolled by one or both of the characteristics of the porosity of theproppant grain or by the addition of a permeable coating on the porousproppant after infusion to further delay the release of the biologicalmarker. When so infused into a porous ceramic proppant, the marker canprovide a tool for the long term diagnostic evaluation of wellperformance.

In order for the biological marker to be reliably carried to the surfacein produced fluid, the biological marker must be capable of eluting fromthe porous proppant grain and partitioning into the produced fluid whichmay be a water-based or hydrocarbon-based fluid. According to severalexemplary embodiments, the biological marker can be encapsulated topreferentially partition into either or both water and hydrocarbonphases, depending on the diagnostic goals. This variable partitioningallows for more definitive diagnostic capabilities. For example, asmentioned above, hydraulic fracturing is often performed in stages. Thatis, the entire hydrocarbon bearing interval to be hydraulicallyfractured is not stimulated at one time but rather in stages. In thecase of a horizontal well as many as 40 separate hydraulic fracturingoperations may be conducted in the horizontal well. Because each stageof hydraulic fracturing entails additional cost, it is of interest todetermine how many of the stages are contributing to production from thewell and further which contributing stages are producing hydrocarbonsand which are producing water.

According to several exemplary embodiments, a biological marker can beused to accomplish this objective. For example, according to severalexemplary embodiments, if a well is hydraulically fractured in fivestages and it is of diagnostic importance to determine which of thestages are producing hydrocarbons and which of the stages are producingwater, then there may be infused into the pores of the porous ceramicproppant for the first stage an unique hydrocarbon-partitioningbiological marker, such as an encapsulated synthetic DNA with a knownsequence. Also, there may be added to the first stage a porous ceramicproppant infused with a unique water-partitioning biological marker. Forthe second stage of the hydraulic fracturing operation, then there maybe infused into the pores of the porous ceramic proppant a differentunique hydrocarbon-partitioning biological marker. Also, there may beadded to the second stage a porous ceramic proppant infused with adifferent, unique water-partitioning biological marker. According toseveral exemplary embodiments, this method of infusing differentuniquely distinguishable hydrocarbon- and water-partitioning biologicalmarkers in the porous ceramic proppants may continue for all or aportion of the subsequent stages. In addition to determining whichstages of a hydraulically fractured well are producing hydrocarbonsand/or water it may be desirable to determine the fraction of thecreated fracture that is contributing to the flow of fluids. Estimatesof the length and heights of the created fracture are possible byvarious means well known to those of ordinary skill in the art. Fracturelengths of several hundred feet and heights of 50 feet or more arecommon. Further it is also well established that the entire length andheight of the created fracture may not contribute to production from thewell. This lack of contribution can be determined by a number of methodswell known to those of ordinary skill in the art. To the extent theentire fracture does not contribute to flow, the cost to create thenon-contributing portion is wasted or conversely failure of a portion ofthe fracture to contribute may result in a reduction of producedhydrocarbons from the well. Thus, it is valuable to assess the fractionof the created fracture contributing to flow. Such knowledge can lead tooptimization of the design of subsequent hydraulic fracturingoperations. This can be accomplished by incorporating a porous ceramicproppant infused with a unique water and/or hydrocarbon partitioningbiological marker within a segment of the proppant being pumped in aparticular stage and then incorporating a porous ceramic proppantinfused with a different unique water and/or hydrocarbon partitioningbiological marker within a second a segment of the proppant being pumpedin the same stage. This method can be replicated for as many segments ofthe stage one desires to interrogate. In the case of a 40 stagehydraulic fracturing operation where it is desirable to determine thecontribution of both hydrocarbons and water from each stage as well asthe hydrocarbon and water contribution from 5 segments of each stage,then 400 unique biological markers are required.

According to several exemplary embodiments, when the well is placed onproduction following the completion of the hydraulic fracturingoperations, the infused biological marker will elute from the porousceramic grains and will partition into one or both of the producedhydrocarbons and water. Samples of the produced water and hydrocarbonsare then captured at different points in time and analyzed for thepresence of the unique biological markers. By identifying the presenceand relative concentration of each of the biological markers, diagnosticdeterminations can be made of the effectiveness of the stimulation andthe hydrocarbon or water productivity of the stimulated formation. Thisdiagnostic information can then be utilized to optimize subsequenthydraulic fracturing operations in nearby wells.

In order to accomplish this, and according to several exemplaryembodiments, the biological marker separates from the porous ceramicproppant after the porous ceramic proppant is injected into thefracture. In several exemplary embodiments, separation of the biologicalmarker from the porous ceramic proppant can be accomplished by thebiological marker leaching, eluting, diffusing, bleeding, discharging,draining, seeping, or leaking out of the porous ceramic proppant, or anycombination thereof. Further, this leaching, eluting, diffusing,bleeding, discharging, draining, seeping, or leaking out of the porousceramic proppant, or any combination thereof can be further controlledby a permeable coating.

As mentioned above, the partitioning of the biological marker, i.e.,whether into the hydrocarbon or water phase, can be tailored based onthe needs of the fracturing operation by tailoring the encapsulationmaterial. If, for example, diagnostic information is needed about ahydrocarbon-producing section of the well, a porous ceramic proppant canbe infused with an encapsulated hydrocarbon-partitioning biologicalmarker, which will then separate from the porous ceramic proppant intothe surrounding hydrocarbon fluids. Conversely, if diagnosticinformation is needed about a water-producing section of the well, aporous ceramic proppant can be infused with an encapsulatedwater-partitioning biological marker, which will then separate from theporous ceramic proppant into the water.

As mentioned above, DNA alone can be used as the biological marker. DNAis typically water-soluble and can be infused into a porous ceramicproppant without any modification in order to function as awater-soluble biological marker. According to several exemplaryembodiments, the DNA can be formulated in such a way that it ishydrocarbon-soluble and will separate into hydrocarbon fluids as well.For example, the water-solubility of DNA is due to the negative chargesassociated with the phosphodiester groups of the DNA. The negativecharges of the phosphodiester structures can be removed by methylation.Methylation of this region of the DNA molecule will ensure that thispart of the molecule becomes hydrophobic, i.e., hydrocarbon-soluble,thereby ensuring that the DNA molecule is soluble in the hydrocarbonphase. Other procedures for formulating hydrocarbon-soluble DNA can befound in U.S. Pat. No. 5,665,538, the entire disclosure of which isherein incorporated by reference.

While DNA itself may be used as a biological marker, the reservoirconditions in which the DNA is placed may not be optimal for the longterm survivability of the DNA. These conditions include reservoirtemperatures exceeding 200° F. and sometimes up to 400° F., as well ashighly saline formation waters. However, numerous DNA encapsulationtechniques are well known to those of ordinary skill in the art and byencapsulating the DNA, its survivability in harsh conditions is greatlyenhanced. The partitioning of the DNA, whether into the hydrocarbon orwater phase, can be tailored by tailoring the encapsulation material.

Additionally, molecules containing specific nucleotide sequences may beselectively used to enhance compatibility with the harsh wellbore andformation temperatures and pressures based on the improved thermalstability displayed by DNA molecules having higher concentrations ofcertain base pairs. Specifically, the DNA molecules having the greatestthermal resistance are those which include higher levels of GC basepairs and lower levels of AT base pairs. For example, the sequence GCAT(with corresponding base pair sequence CGTA) shows thermal stability attemperatures of from about 186 to 221° F. The sequence GCGC (withcorresponding base pair sequence CGCG) is thermally resistant attemperatures of up to about 269 to 292° F. Conversely, the inclusion ofhigher levels of AT base pairs reduces thermal stability. For example,some thymine in the combination reduces the stability such that thesequence ATCG (with corresponding base pair sequence TAGC) only survivesat temperatures of up to about 222 to 250° F., while the sequence TATA(with corresponding base pair sequence ATAT) is thermally stable attemperatures of up to only about 129 to 175° F. In addition, if the DNAmolecules that include the sequence ATCG (with corresponding base pairsequence TAGC) are manipulated to include a modification known asG-clamp, the thermal stability increases by an additional 32° F. or fromtemperatures of up to about 254 to 282° F. As shown below, the G-clampmodification involves adding a tricyclic analogue of cytosine giving theduplex base pair (G-C) an additional hydrogen bond.

By increasing the hydrogen bonding of the duplex base pair from 3 to 4,the thermal stability increases by an additional 32° F.

The DNA can be either single stranded or double stranded. The naturalorientation of DNA in the double stranded version is the Watson-Crickpairing. Synthetic DNA, however, is not constrained in the same way asnatural DNA. Still, the indicator of thermal stability is athermodynamic reorientation of the strands and consists primarily of thestrands separating into two single strands. This is known as melting andhappens over a narrow temperature range. What has been observed is thatthe DNA of some organisms resists this thermal collapse, examples beingcertain thermophilic organisms. Analysis of their genomes gives a directcorrelation between the levels of G-C DNA in the sequences. Essentially,thermal stability is directly related to the number of hydrogen bondsbetween the bases in the duplex pairs. However, the stacking (pairing inthe double strands) is also a factor. It has been determined that animportant feature of thermal stability in natural DNA relies heavilyupon the molar ratio of G-C pairing since this gives the highest densityof hydrogen bonds. Thermal stability ultimately depends upon theso-called melting point where the strands of a double stranded DNAseparate. This has no significance to single stranded synthetic DNA,however, which is already separated. The separation of the strands ofdouble stranded DNA which occurs at the melting point is to some extentreversible. The strands can re-join once the temperature dropssufficiently. The thermal stability depends upon the thermal resistanceof the base pairs or duplex units as well as the stacking forces whichjoin the strands of double stranded DNA. As noted above, thermalstability can also be improved by modifying the molecular arrangementwithin a particular base pair. For instance, in addition to theG-G-Clamp modification noted above, the thermal stability of an A-T basepair can be improved, as shown below, by modifying the adenine-thyminebase pair to include a 2-aminoadenine-T complex which increases thehydrogen bonding in the complex from 2 to 3 and increases its thermalstability by about 5° F.

The thermal stability of specific base pairs can be used to generate athermodynamic assessment of potential. As noted above, reasonablechemical modifications can extend this thermal range and retain theessential features of DNA for the purposes of measurement. The chemicalnature of DNA means that it is susceptible to hydrolysis and the rate ofhydrolysis increases with increasing temperature. Hydrolysis is anotherroute for the decomposition of DNA in addition to decomposition due toits melting behavior as discussed above. That said, it is known that anumber of organisms survive extremes of temperature which means thattheir genetic material must have some inherent thermal stability. Thisresponse has been directly correlated to the molar fraction of G-C basepairs irrespective of whether such base pairs are present as single ordouble strands. Natural DNA, however, is chromosomal and so must bedouble stranded.

Also it has been shown that the repetition of the G-C duplex appears toimpart more stability since it has a direct effect upon the thermalresistance of the DNA. This shows how various organisms cope with hightemperature by incorporating a larger G-C molar fraction into theirgenome. It appears that the molar fraction of G-C is the key rather thanany weak link, which might be incorporated into the sequence. Chainterminators appear to have little overall effect on the thermalstability of the DNA. Essentially, what this means is that the molarfraction of certain base pairs in the DNA sequence can be variedaccording to the temperature range required. Getting down to the detailof destruction reactions for the DNA sequence will depend upon theenvironment to which a particular DNA sequence will be subjected and theexposure to hydrolysis reactions are an area of concern. However themodifications of the base pairs discussed above which can be introducedwhile still retaining the inherent features which make DNA an idealtracer offer clear routes for tailor-made tracers for oilfield use.

Selectively using a specific DNA molecule as a biological marker basedon its thermal stability properties allows for the use of DNA as abiological marker over a far wider range of conditions than is currentlypossible. Further, the survival of the DNA molecules at highertemperatures allows for accurate detection even with very low levels ofDNA present in the formation by avoiding degradation of the DNA.Additionally, the diverse number of unique DNA molecules vastly adds tothe number of unique tracers which can be applied in the oilfield,thereby greatly increasing both the range and diversity of oilfieldoperations to which biological markers can be applied and greatlyimproving the knowledge and understanding of increasingly complex wellsand their behavior. This knowledge will lead to better completion andstimulation practices resulting in cost savings and improved wellperformance.

In several exemplary embodiments, a DNA molecule exhibiting specificthermostability properties, based on its specific nitrogenous basecomposition that are compatible with the thermal environment of aspecific well, may be selectively infused into a porous proppant to beused in the well operations according to the methods and embodimentsdescribed herein. For example, for wells exhibiting temperatures of upto about 269 to 292° F., a DNA molecule containing the GCGC sequencecould be synthesized and infused into the proppant to be injected intothe well formation. This DNA molecule would better withstand the thermalconditions of the well, thereby allowing it to be more effectively usedas a biological marker that conveys information regarding well formationand production.

According to several exemplary embodiments, the chemical treatmentagent, such as a biological marker separates from the porous ceramicproppant continuously over a period of up to about one year, up to aboutfive years, or up to about ten years after placement of the proppant inthe hydraulically created fracture. Systems, techniques and compositionsfor providing for the sustained release of DNA are well known to thoseof ordinary skill in the art. For example, European Patent No.1,510,224, the entire disclosure of which is incorporated herein byreference, discloses several methods for enabling the sustained releaseof DNA over a period of time. According to several exemplaryembodiments, DNA is encapsulated with a polymer or a material infusedwith DNA is coated with a permeable nondegradable coating. In severalexemplary embodiments, the encapsulating polymer includes one or more ofhigh melting acrylate-, methacrylate- or styrene-based polymers, blockcopolymers of polylactic-polyglycolic acid, polyglycolics, polylactides,polylactic acid, gelatin, water-soluble polymers, cross-linkablewater-soluble polymers, lipids, gels, silicas, or other suitableencapsulating materials. Additionally, the encapsulating polymer mayinclude an encapsulating material that comprises a linear polymercontaining degradable co-monomers or a cross-linked polymer containingdegradable cross-linkers.

According to several exemplary embodiments, after the chemical treatmentagent, such as a biological marker separates from the porous ceramicproppant and partitions into a production fluid, the production fluidwill then transport the biological marker to the surface. Once theproduction fluids reach the surface, the fluids can be analyzed for thepresence of the biological marker.

According to several exemplary embodiments, the chemical treatmentincludes one or more biological markers having unique identifiers andthe unique identifier of the one or more biological markers is loggedbefore the one or more markers is injected into the fracture. In severalexemplary embodiments when multiple biological markers are used acrossone or all of the stages of a fracture, this log will enable the welloperator to match the biological marker in the production fluid to thesection of the fracture where it was produced. For example, if threeunique DNA markers are injected into stages 1, 2, and 3, respectively,of a hydraulic fracturing stimulation operation, the unique identifyingbase sequence of each DNA marker injected into stages 1, 2, and 3 willbe recorded. If DNA is detected in the production fluids at the surface,the sequence of the returned DNA can be compared to the log to determinewhich stage produced the DNA. Relative amounts of each marker can beused to quantitatively estimate the relative volumes of the producedfluids from each of the stages. Identification and detection of DNAsequences is well known in the art and many companies manufacture“off-the-shelf” identification and detection assays. For example, DNAdetection and identification assays and kits are available commerciallyfrom Molecular Devices, LLC and Illumina, Inc. Further, DNA replicationmethodologies are well known to those of ordinary skill in the art. Thispermits extremely low levels of DNA present in the produced fluids,which may be below detection limits, to be identified by first employinga replication procedure to increase the concentration of the DNA beyonddetection limits. Because the replication methods proportionallyincrease all DNA present, the relative amount of the individual DNAmarkers present is not altered.

According to several exemplary embodiments, once the biological markersare recovered from the production fluids and identified, a comparativeanalysis of the amount of biological marker from each stage or stagesegment in the sample can then be related to the amount of hydrocarbonor water produced from that section. For example, the relativehydrocarbon or water volume contribution of a stage or stages of theformation can be estimated based on the amount of biological markersrecovered, i.e. with more hydrocarbon or water produced from that stageresulting in more biological detection from that stage. Additionally,the relative hydrocarbon or water volume contribution of a segment of astage can be estimated based on the amount of biological markersrecovered from the segment of the stage. Based on this analysis, adiagnostic log across multiple stages of a fractured formation can bedeveloped, giving a well operator detailed knowledge about theproduction volume (or lack thereof) of the entire fractured formation.This analysis can likewise be repeated periodically over an extendedtimeframe to establish trends in the production performance of the wellproviding diagnostic information that is not now available with existingtechnologies.

In another aspect of the invention, an exemplary composition isprovided. The composition includes a porous ceramic proppant infusedwith a chemical treatment agent, such as a biological marker, asdescribed herein.

According to several exemplary embodiments, the chemically infusedcoated porous ceramic proppant is prepared according to a two-stepprocess. In the first step, a chemical treatment agent is infused intothe porous ceramic particulates. In the second step, the infused porousceramic particulates are coated with a semi-permeable substantiallynon-degradable polymer. In several exemplary embodiments, the chemicaltreatment agent is infused into the porous ceramic particulates byvacuum infusion. In other exemplary embodiments, the chemical treatmentagent is infused into the porous ceramic particulates using a thermalinfusion process whereby the porous ceramic particulates are heated andwetted with a solution containing the chemical treatment agent. As theporous ceramic particulates cool, capillary action causes the chemicaltreatment agent to infuse into the porous ceramic particulates.

According to several exemplary embodiments, the chemically infusedcoated porous ceramic proppant is prepared according to a one stepprocess. According to the one step process, the porous ceramicparticulates are infused with a chemical treatment agent using thethermal infusion process described above and coated with asemi-permeable substantially non-degradable polymer before the resultantheat from the thermal infusion process dissipates.

According to several exemplary embodiments, a composite ceramic proppantcomposition for use in hydraulic fracturing is produced. According toseveral exemplary embodiments, the composite ceramic proppantcomposition includes porous ceramic particulates infused with a chemicaltreatment agent without the use of a solvent. Furthermore, according toseveral exemplary embodiments, the infused porous ceramic particulatesare coated with a semi-permeable substantially non-degradable polymer.

According to several exemplary embodiments, suitable proppant materialsfor use as the porous ceramic particulates, suitable chemical treatmentagents, and suitable polymer coatings include those listed above.

According to several exemplary embodiments, the chemical treatment agentis infused into the porous ceramic particulates without the use of asolvent by melting, thawing, heating, softening, or warming the chemicaltreatment agent to a sufficiently low viscosity to allow infusion intothe porous ceramic particulates. In several exemplary embodiments, asufficiently low viscosity to allow infusion into the porous ceramicparticulate is from about 1000-10,000 centipoise (cps), from about1000-5,000 cps, or from about 1000-2500 cps.

According to several exemplary embodiments, after the chemical treatmentagent is melted to a sufficiently low viscosity to allow infusion intothe porous ceramic particulates, the melted chemical treatment agent isinfused into the porous ceramic particulates using the infusion methodsdescribed above.

According to several exemplary embodiments, a method of fracturing asubterranean formation includes injecting a hydraulic fluid into thesubterranean formation at a rate and pressure sufficient to open afracture therein, and a fluid containing a proppant compositioncomprising porous ceramic particulates infused with a chemical treatmentagent and coated with a semi-permeable substantially non-degradablepolymer, as described herein and having one or more of the properties asdescribed herein is injected into the fracture to prop the fracture inan open condition.

According to several exemplary embodiments, a method of fracturing asubterranean formation includes injecting a hydraulic fluid into thesubterranean formation at a rate and pressure sufficient to open afracture therein, and a fluid containing a proppant compositioncomprising porous ceramic particulates infused with a chemical treatmentagent without the use of a solvent, as described herein and having oneor more of the properties as described herein is injected into thefracture to prop the fracture in an open condition.

The following examples are illustrative of the compositions and methodsdiscussed above.

EXAMPLES

The examples following below were carried out using exemplary materialsin order to determine the elution rate of DTPMP (diethylenetriaminepenta(methylene phosphonic acid)), a corrosion and scale inhibitor, fromporous proppant infused with DTPMP and coated with various polymers andcompared to uncoated porous proppant infused with DTPMP. These examplesare meant to be illustrative of exemplary embodiments of the presentinvention and are not intended to be exhaustive.

Example 1

Four 500 gram batches of 20/40 CARBO UltraLite, an ultra-lightweightceramic proppant having an ASG of 2.71 and having a porosity of 20-25%that is commercially available from CARBO Ceramics, Inc., were eachinfused with a diethylenetriamine penta(methylene phosphonic acid)(“DTPMP”) solution having a solids content of 41%, which is commerciallyavailable from Riteks, Inc., and were then coated with a semi-permeablesubstantially non-degradable polymer in a two-step process as describedbelow.

Each batch of proppant was heated in an oven set to 482° F. (250° C.)for approximately one hour. The heated batches of proppant were thenremoved from the oven and allowed to cool until they reached atemperature of between 430-440° F. as monitored by a thermocouple. Oncethe proppant batches reached the desired temperature, 64.2 grams of theDTPMP solution was added to each batch and allowed to infuse into theproppant particulates for approximately three minutes, such that theDTPMP constituted 5% by weight of the infused proppant. After theproppant particulates were infused with DTPMP, each batch was coatedwith a semi-permeable substantially non-degradable polymer.

The Batch 1 proppant was coated according to the following procedurewith a phenol formaldehyde standard reactivity resin that iscommercially available from Plastics Engineering Company under the tradename Plenco 14870. Compared to the other phenol formaldehyde resinsdiscussed below, the Plenco 14870 resin had a relatively low viscosityof about 1100 cps at 150° C. After the coating procedure, the Batch 1proppant included 2% by weight of the polymeric coating.

The Batch 1 proppant was placed in a heated mixing bowl and wasmonitored with a thermocouple until the proppant reached a temperatureof between 410-420° F. When the proppant reached the desiredtemperature, 8.08 grams of the phenol formaldehyde resin was added tothe proppant and allowed to melt and spread over the proppant forapproximately 45 seconds. Next, 2.63 grams of a 40%hexamethylenetetramine (which is also known as and will be referred toherein as “hexamine”), solution, and which is commercially availablefrom The Chemical Company, was added to crosslink and cure the phenolformaldehyde resin and was allowed to mix for 1 minute and 25 seconds.Finally, 1.2 grams of a 50-60% cocoamidopropyl hydroxysultainesurfactant, which is commercially available from The LubrizolCorporation under the trade name “Chembetaine™ CAS”, was added andallowed to mix for 1 minute.

The Batch 2 proppant was coated according to the following procedurewith a phenol formaldehyde highly reactive, high viscosity polymer resinthat is commercially available from Plastics Engineering Company underthe trade name Plenco 14750. Compared to the other phenol formaldehyderesins discussed above and below, the Plenco 14750 resin had arelatively high viscosity of about 34,900 cps at 150° C. After thecoating procedure, the Batch 2 proppant included 2% by weight of thepolymeric coating.

The Batch 2 proppant was placed in a heated mixing bowl and wasmonitored with a thermocouple until the proppant reached a temperatureof between 410-420° F. When the proppant reached the desiredtemperature, 8.08 grams of the phenol formaldehyde resin was added tothe proppant and allowed to melt and spread over the proppant forapproximately 45 seconds. Next, 2.63 grams of a 40% hexamine solution,which is commercially available from The Chemical Company, was added tocrosslink and cure the phenol formaldehyde resin and was allowed to mixfor 1 minute and 25 seconds. Finally, 1.2 grams of a 50-60%cocoamidopropyl hydroxysultaine surfactant, which is commerciallyavailable from The Lubrizol Corporation under the trade name“Chembetaine™ CAS”, was added and allowed to mix for 1 minute.

The Batch 3 proppant was coated according to the following procedurewith the phenol formaldehyde highly reactive, high viscosity polymerresin mentioned above that is commercially available from PlasticsEngineering Company under the trade name Plenco 14750. As discussedabove, the Plenco 14750 resin had a relatively high viscosity of about34,900 cps at 150° C. After the coating procedure, the Batch 3 proppantincluded 4% by weight of the polymeric coating.

The Batch 3 proppant was placed in a heated mixing bowl and wasmonitored with a thermocouple until the proppant reached a temperatureof between 410-420° F. When the proppant reached the desiredtemperature, 17.61 grams of the phenol formaldehyde resin was added tothe proppant and allowed to melt and spread over the proppant forapproximately 45 seconds. Next, 5.72 grams of a 40% hexamine solution,which is commercially available from The Chemical Company, was added tocrosslink and cure the phenol formaldehyde resin and was allowed to mixfor 1 minute and 25 seconds. Finally, 1.2 grams of a 50-60%cocoamidopropyl hydroxysultaine surfactant, which is commerciallyavailable from The Lubrizol Corporation under the trade name“Chembetaine™ CAS”, was added and allowed to mix for 1 minute.

The Batch 4 proppant was coated according to the following procedurewith a polyurethane polymer that is made by reacting a polyisocyanateresin with a curing agent both of which are commercially available fromAir Products, Inc. under the trade names ANCAREZ® ISO HDiT and AMICURE®IC221, respectively. After the coating procedure, the Batch 4 proppantincluded 4% by weight of the polyurethane polymeric coating.

The Batch 4 proppant was placed in a mixing bowl that was maintained atroom temperature. At room temperature, 13.5 grams of the curing agentAMICURE® IC221 was added to the proppant batch and mixed for one minute.After one minute, 7.2 grams of the ANCAREZ® ISO HDiT polyisocyanateresin was added to the proppant batch and mixed with the proppant forapproximately 5 minutes.

A fifth proppant batch was then prepared that included 1000 grams of20/40 CARBO UltraLite ceramic proppant. The Batch 5 proppant was infusedwith DTPMP and coated in a one-step thermal infusion process with aphenol formaldehyde highly reactive, low viscosity polymer resin that iscommercially available from Plastics Engineering Company under the tradename Plenco 14862. Compared to the other phenol formaldehyde resinsdiscussed above and below, the Plenco 14862 resin had a relatively lowviscosity of about 1080 cps at 150° C. After the one-step thermalinfusion process, the Batch 5 proppant included 2% by weight of thepolymeric coating.

The Batch 5 ceramic proppant was heated in an oven set to 482° F. (250°C.) for approximately one hour. The heated batch of proppant was thenremoved from the oven and allowed to cool until it reached a temperatureof between 430-440° F. as monitored by a thermocouple. Once the proppantbatch reached the desired temperature, 128.4 grams of the DTPMP solutionwas added to the batch and allowed to infuse into the proppantparticulates for approximately 5 seconds, such that the DTPMPconstituted 5% by weight of the infused proppant. After 5 seconds hadelapsed, 17.35 grams of the phenol formaldehyde, high reactivity, lowviscosity polymer resin (Plenco 14862) was added to the proppant batch.After another 5 seconds had elapsed, 5.64 grams of a 40% hexaminesolution, which is commercially available from The Chemical Company, wasadded to crosslink and cure the phenol formaldehyde resin and wasallowed to mix for 10 minutes and 15 seconds. Finally, 1.2 grams of a50-60% cocoamidopropyl hydroxysultaine surfactant, which is commerciallyavailable from The Lubrizol Corporation under the trade name“Chembetaine™ CAS”, was added and allowed to mix for another 30 seconds.

Finally, a sixth proppant batch was prepared as a control. The Batch 6control proppant batch, included 1000 grams of 20/40 CARBO UltraLiteceramic proppant and was infused with DTPMP but did not include apolymeric coating.

The Batch 6 ceramic proppant was heated in an oven set to 482° F. (250°C.) for approximately one hour. The heated batch of proppant was thenremoved from the oven and allowed to cool until it reached a temperatureof between 430-440° F. as monitored by a thermocouple. Once the proppantbatch reached the desired temperature, 241.8 grams of the DTPMP solutionwas added to the batch and allowed to infuse into the proppantparticulates for approximately 3 minutes, such that the DTPMPconstituted 9% by weight of the infused proppant.

Table 1 below represents the 6 batches prepared for Example 1.

TABLE 1 Example 1 Batches Batch Number Infusant/Polymer Coating Batch 15% by weight DTPMP, 2% by weight phenol formaldehyde, standardreactivity, low viscosity (Plenco 14870) Batch 2 5% by weight DTPMP, 2%by weight phenol formaldehyde, high reactivity, high viscosity (Plenco14750) Batch 3 5% by weight DTPMP, 4% by weight phenol formaldehyde,high reactivity, high viscosity (Plenco 14750) Batch 4 5% by weightDTPMP, 4% by weight polyurethane Batch 5 5% by weight DTPMP, 2% byweight phenol formaldehyde, high reactivity, low viscosity (Plenco14862) Batch 6 9% by weight DTPMP, no coating

Proppant Batches 1-6 were then placed in a seawater eluent for one hour.The seawater eluent was prepared according to the ASTM D1141-98(2013)procedure and had the composition shown below in Table 2.

TABLE 2 ION CONC. ION & SALT (mg/L) K⁺ as KCl 403.0 Mg²⁺ as MgCl₂•6H₂O657.0 Na⁺ as NaCl 10025.6 HCO₃ ⁻ as NaHCO₃ 159.0 Na⁺ as NaHCO₃ 59.9 SO₄²⁻ as Fe₂SO₄•7H₂O 0.0 SO₄ ²⁻ as Na₂SO₄•10H₂O 1308.0 Na⁺ as Na₂SO₄•10H₂O626.1 Ca²⁺ as CaCl₂•2H₂O 329.0 Sr²⁺ as SrCl₂•6H₂O 7.0 Ba²⁺ as BaCl₂•2H₂O0.0 Fe(II) as FeCl₂•4H₂O 0.0 Fe(II) as FeSO₄•7H₂O 0.0 CH₃COO⁻ asCH₃COONa•3H₂O 1.0 Na⁺ as CH₃COONa 0.4 Total SO₄ ²⁻ 1308.0 Total Na⁺10712.0 Cl⁻ from analysis (mg/L) = 18330.0 Cl⁻ from calculation (mg/L) =18330.0 Error (%) = 0.00% Total Salt Weight (mg/L) = 37591 SaltConcentration (%) = 3.76%

After one hour, the eluent was tested for the amount of DTPMP (in partsper million, ppm) present. For each of proppant Batches 1-5, the eluentwas subsequently tested for the presence of DTPMP at 2, 3, 6, 25, 27.5,29.5, and 97.5 hours, respectively. For proppant Batch 1, the eluent wasadditionally tested for the presence of DTPMP at 100, 102, 104.5 and120.5 hours. For Batch 6, the eluent was subsequently tested for thepresence of DTPMP at 2, 3, 4, 5, 21, 22, 23, 24, 26, 27, 28, 29, 44, 47,49, 53, 70 and 74 hours.

The amount of DTPMP in ppm detected in the eluent was plotted as afunction of time to obtain the elution profile curves shown in FIG. 3.In FIG. 3, a line has been drawn at 6 ppm which represents the minimumeffective concentration of DTPMP as a corrosion and scale inhibitor. Byplotting the amount of detected DTPMP in the eluent versus time forproppant Batches 1-6 and comparing these results with the 6 ppm line,the length of time a particular proppant batch elutes an effectiveamount of DTPMP can be determined.

FIG. 3 clearly shows that proppant Batches 1-5 which included asemi-permeable substantially non-degradable polymeric coating eluted aneffective amount of DTPMP for a longer period of time compared toproppant Batch 6 which did not include a semi-permeable substantiallynon-degradable polymeric coating. FIG. 3 also clearly shows that for thethree proppant batches that were infused with 5% by weight of DTPMP andcoated with 2% by weight of phenol formaldehyde according to thetwo-step process, namely proppant Batches 1-3, the lower the viscosityof the resin used to make the phenol formaldehyde polymeric coating, thelonger the period of time in which an effective amount of DTPMP waseluted. In addition, FIG. 3 shows that when phenol formaldehyde resinshaving relatively low viscosity are used to prepare the polymericcoating, the proppant coated according to the two-step process (Batch 1)eluted an effective amount of DTPMP for a longer period of time comparedto proppant coated according to the one-step process (Batch 5). Finally,FIG. 3 shows that for the three proppant batches that were infused with5% by weight of DTPMP and coated with 2% or 4% by weight of phenolformaldehyde according to the two-step process, namely proppant Batches1-3, an effective amount of DTPMP was eluted for a longer period of timecompared to proppant that was infused with 5% by weight of DTPMP andcoated with 2% by weight of polyurethane according to the two-stepprocess.

Example 2

Three 1000 pound plant batches of 20/40 CARBO UltraLite, referred tobelow as Batches 7-9, were infused with the DTPMP solution mentionedabove in Example 1 and were then coated according to the followingprocedure with a phenol formaldehyde standard reactivity resin that iscommercially available from Plastics Engineering Company under the tradename Plenco 14941. Compared to the other phenol formaldehyde resinsdiscussed above, the Plenco 14941 resin had a relatively mediumviscosity of about 1850 cps at 150° C.

Each of Batches 7-9 were infused with 183.6 pounds of the DTPMPsolution, such that the DTPMP constituted 7% by weight of the infusedproppant. The proppant of Batches 7-9 was then coated with the phenolformaldehyde standard reactivity, medium viscosity polymer resin (Plenco14941), in a two-step process. After the two-step process, the Batch 7proppant included 0.5% by weight of the polymeric coating, the Batch 8proppant included 1.0% by weight of the polymeric coating and the Batch9 proppant included 2.0% by weight of the polymeric coating.

After the proppant particulates were infused with 7% DTPMP, each batchwas coated with a different amount of the same semi-permeablesubstantially non-degradable polymer. The Batch 7 proppant was heated to415° F. When the proppant reached the desired temperature, 6.6 pounds ofthe phenol formaldehyde, standard reactivity, medium viscosity polymerresin (Plenco 14941) was added to the proppant and allowed to melt andspread over the proppant for approximately 45 seconds. Next, 2.8 poundsof a 30% hexamine solution, and which is commercially available from TheChemical Company, was added to crosslink and cure the phenolformaldehyde resin and was allowed to mix for 25 seconds. Finally, 0.5pound of a 50-60% cocoamidopropyl hydroxysultaine surfactant, which iscommercially available from The Lubrizol Corporation under the tradename “Chembetaine™ CAS” was added and allowed to mix.

The Batch 8 proppant was heated to 415° F. When the proppant reached thedesired temperature, 12.3 pounds of the phenol formaldehyde, standardreactivity, medium viscosity polymer resin (Plenco 14941) was added tothe proppant and allowed to melt and spread over the proppant forapproximately 45 seconds. Next, 5.2 pounds of a 30% hexamine solution,and which is commercially available from The Chemical Company, was addedto crosslink and cure the phenol formaldehyde resin and was allowed tomix for 25 seconds. Finally, 0.5 pound of a 50-60% cocoamidopropylhydroxysultaine surfactant, which is commercially available from TheLubrizol Corporation under the trade name “Chembetaine™ CAS” was addedand allowed to mix.

The Batch 9 proppant was heated to 415° F. When the proppant reached thedesired temperature, 22.7 pounds of the phenol formaldehyde, standardreactivity, medium viscosity polymer resin (Plenco 14941) was added tothe proppant and allowed to melt and spread over the proppant forapproximately 45 seconds. Next, 9.7 pounds of a 30% hexamine solution,and which is commercially available from The Chemical Company, was addedto crosslink and cure the phenol formaldehyde resin and was allowed tomix for 25 seconds. Finally, 0.5 pounds of a 50-60% cocoamidopropylhydroxysultaine surfactant, which is commercially available from TheLubrizol Corporation under the trade name “Chembetaine™ CAS” was addedand allowed to mix.

Proppant Batches 7-9 of Example 2 were compared with proppant Batches 1,2 and 6 from Example 1, as indicated in Table 3 below.

TABLE 3 Example 2 Batches Batch Number Infusant/Polymer Coating Batch 1(from Example 1) 5% by weight DTPMP, 2% by weight phenol formaldehyde,standard reactivity, low viscosity (Plenco 14870) Batch 2 (fromExample 1) 5% by weight DTPMP, 2% by weight phenol formaldehyde, highreactivity, high viscosity (Plenco 14750) Batch 6 (from Example 1) 9% byweight DTPMP, no coating Batch 7 7% by weight DTPMP, 0.5% by weightphenol formaldehyde, standard reactivity, medium viscosity (Plenco14941) Batch 8 7% by weight DTPMP, 1.0% by weight phenol formaldehyde,standard reactivity, medium viscosity (Plenco 14941) Batch 9 7% byweight DTPMP, 2.0% by weight phenol formaldehyde, standard reactivity,medium viscosity (Plenco 14941)

Proppant Batches 7-9 were then placed in a seawater eluent for one hour.The seawater eluent was prepared according to the ASTM D1141-98(2013)procedure and had the composition shown above in Table 2. After onehour, the eluent was tested for the amount of DTPMP present. The eluentwas subsequently tested for the presence of DTPMP at 2, 3, 4, 5, 6, 7,8, 25, 29, 33, and 48.5 hours, respectively. For proppant Batch 9, theeluent was additionally tested for the presence of DTPMP at 53.5 and55.5 hours. For Batches 1, 2 and 6, the eluent was subsequently testedfor the presence of DTPMP as described above in Example 1.

The amount of DTPMP in ppm detected in the eluent for Batches 7-9 wasplotted with the data from Batches 1, 2 and 6 from Example 1 as afunction of time to obtain the elution profile curves shown in FIG. 4.In FIG. 4, a line has been drawn at 6 ppm which represents the minimumeffective concentration of DTPMP as a corrosion and scale inhibitor. Byplotting the amount of detected DTPMP in the eluent versus time forproppant Batches 1-2 and 6-9 and comparing these results with the 6 ppmline, the length of time a particular proppant batch elutes an effectiveamount of DTPMP can be determined.

FIG. 4 clearly shows that proppant Batches 7-9 which included asemi-permeable substantially non-degradable polymeric coating eluted aneffective amount of DTPMP for a longer period of time compared toproppant Batch 6 which did not include a semi-permeable substantiallynon-degradable polymeric coating. In addition, FIG. 4 clearly shows thatfor the three proppant batches that were infused with 7% by weight ofDTPMP and coated with 0.5%, 1.0% and 2.0% by weight of phenolformaldehyde according to the two-step process, namely proppant Batches7-9, an effective amount of DTPMP was eluted for a longer period of timethe higher the percent by weight of the phenol formaldehyde polymericcoating.

Example 3

A 500 gram batch of 20/40 CARBO UltraLite, referred to below as Batch 10was infused with 64.2 grams of the DTPMP solution mentioned above inExample 1, such that the DTPMP constituted 5% by weight of the infusedproppant and was then coated with polylactic acid such that the finalproduct included 2% by weight of the polylactic acid coating in atwo-step thermal process. Polylactic acid is a degradable polymericcoating that is commercially available from Danimer under the trade nameof “92938”. 500 grams of the 20/40 CARBO UltraLite was heated in an ovenset at 250° C. for one hour. 64.2 grams of the DTPMP solution was addedto the heated proppant and allowed to mix for 3 minutes. The infusedproppant was then heated to 193° C. and 51.0 grams of the polylacticacid polymer resin was added to the batch and allowed to mix forapproximately ten minutes.

A 500 gram batch of 20/40 CARBO UltraLite, referred to below as Batch 11was infused with DTPMP and coated with a polyurethane coating accordingto the procedure discussed above, except that 3.6 grams of the AncarezISO HDiT polyisocyanate polymer resin was used to result in a 2% byweight coating of polyurethane.

Proppant Batches 10 and 11 were compared with proppant Batches 1 and 6from Example 1, as indicated in Table 4 below.

TABLE 4 Example 3 Batches Batch Number Infusant/Polymer Coating Batch 15% by weight DTPMP, 2% by weight phenol formaldehyde, standardreactivity, low viscosity (Plenco 14870) Batch 6 5% by weight DTPMP, nocoating Batch 10 5% by weight DTPMP, 2% by weight polylactic acid Batch11 5% by weight DTPMP, 2% by weight polyurethane

Proppant Batches 1, 6, 10 and 11 were then placed in a seawater eluentfor one hour. The seawater eluent was prepared according to the ASTMD1141-98(2013) procedure and had the composition shown above in Table 2.After one hour, the eluent was tested for the amount of DTPMP present.The eluent was subsequently tested for the presence of DTPMP at 2, 3, 4,5, 21, 22, 23, 24, 26, 27, 28, 29, 44, 47, 49, 53, 70 and 74 hours,respectively. For proppant Batch 1, the eluent was additionally testedfor the presence of DTPMP at 93, 98, 165, 173, 189.5, 197.5 and 218hours.

The amount of DTPMP in ppm detected in the eluent was plotted as afunction of time to obtain the elution profile curves shown in FIG. 5.In FIG. 5, a line has been drawn at 6 ppm which represents the minimumeffective concentration of DTPMP as a corrosion and scale inhibitor. Byplotting the amount of detected DTPMP in the eluent versus time forproppant Batches 1, 6, 10 and 11 and comparing these results with the 6ppm line, the length of time a particular proppant batch elutes aneffective amount of DTPMP can be determined.

FIG. 5 clearly shows that proppant Batch 1 which was infused with 5% byweight of DTPMP and coated with 2% by weight of phenol formaldehydeaccording to the two-step process eluted an effective amount of DTPMPfor a longer period of time compared to proppant Batches 10 and 11 whichwere infused with 5% by weight of DTPMP and coated with 2.0% by weightof polylactic acid and polyurethane, respectively. In addition, FIG. 5shows that proppant Batches 10 and 11 which included a degradable and asemi-permeable substantially non-degradable polymeric coating,respectively, eluted an effective amount of DTPMP for a longer period oftime compared to proppant Batch 6 which did not include a semi-permeablesubstantially non-degradable polymeric coating. FIG. 5 also shows thatsubstantially similar results were obtained for proppant Batch 10, thatwas infused with 5% by weight of DTPMP and coated with 2.0% by weight ofpolylactic acid, a degradable polymer and proppant Batch 11 that wasinfused with 5% by weight of DTPMP and coated with 2.0% by weight ofpolyurethane, a semi-permeable substantially non-degradable polymer.

The above results show that proppants coated with a semi-permeablesubstantially non-degradable polymer, like phenol formaldehyde andpolyurethane, release effective amounts of chemical treatment agentslike DTPMP for a longer period of time than typical degradable coatingsor proppant without any coating at all.

While the present invention has been described in terms of severalexemplary embodiments, those of ordinary skill in the art will recognizethat the invention can be practiced with modification within the spiritand scope of the appended claims.

The present disclosure has been described relative to a severalexemplary embodiments. Improvements or modifications that becomeapparent to persons of ordinary skill in the art only after reading thisdisclosure are deemed within the spirit and scope of the application. Itis understood that several modifications, changes and substitutions areintended in the foregoing disclosure and in some instances some featuresof the invention will be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theinvention.

What is claimed is:
 1. A method of making coated and infused porousparticulates having a cured polymer coating, the method comprising:providing a plurality of porous particulates, each having an internalinterconnected porosity of from about 5% to about 35%; heating theplurality of porous particulates; cooling the plurality of porousparticulates to a temperature from 430° F. to 440° F.; contacting theplurality of porous particulates at the temperature of 430° F. to 440°F. with a chemical treatment agent; cooling the plurality of porousparticulates to provide infused porous particulates having a temperaturefrom 410° F. to 420° F.; contacting the infused porous particulates atthe temperature from 410° F. to 420° F. with a phenol formaldehydepolymer to provide an infused porous particulate having a polymercoating; and reacting the polymer coating with hexamine to crosslink thephenol formaldehyde polymer to provide the coated and infused porousparticulates having a cured polymer coating.
 2. The method of claim 1,wherein the cured polymer coating is a semi-permeable substantiallynon-degradable polymer configured to permit the chemical treatment agentto elute therethrough.
 3. The method of claim 1, wherein the chemicaltreatment agent comprises a scale inhibitor, a hydrate inhibitor, ahydrogen sulfide scavenging material, a corrosion inhibitor, a paraffininhibitor, an asphaltene inhibitor, an organic deposition inhibitor, abiocide, a demulsifier, a defoamer, a gel breaker, a salt inhibitor, anoxygen scavenger, an iron sulfide scavenger, an iron scavenger, or aclay stabilizer, or a combination thereof.
 4. The composition of claim1, wherein the phenol formaldehyde polymer has a viscosity of from about1100 cps to about 1850 cps at 150° C.
 5. The composition of claim 1,wherein the chemical treatment agent comprises a chemical tracer.
 6. Thecomposition of claim 5, wherein the chemical tracer comprises abiological marker.
 7. The composition of claim 6, wherein the biologicalmarker comprises deoxyribose nucleic acid (DNA).
 8. A method of makinginfused porous particulates having an epoxy resin coating, comprising:providing a plurality of porous particulates, each having an internalinterconnected porosity of from about 5% to about 35%; heating theplurality of porous particulates; cooling the plurality of porousparticulates to a temperature from 430° F. to 440° F.; contacting theplurality of porous particulates at the temperature of 430° F. to 440°F. with a hydrocarbon soluble chemical treatment agent; cooling theplurality of porous particulates to induce capillary action causing thechemical treatment agent to infuse into the internal interconnectedporosity of the porous particulates without the use of a solvent toprovide infused porous particulates having a temperature from 410° F. to420° F.; and contacting the infused porous particulates at thetemperature of 410° F. to 420° F. with an epoxy resin, causing the epoxyresin to coat the infused porous particulates to provide the infusedporous particulates having the epoxy resin coating.
 9. The method ofclaim 8, wherein the epoxy resin coating is a semi-permeablesubstantially non-degradable polymer configured to permit the chemicaltreatment agent to elute therethrough.
 10. The method of claim 9,wherein the chemical treatment agent comprises a paraffin inhibitor. 11.The method of claim 10, wherein the chemical treatment agent comprisesethylene vinyl acetate copolymers.
 12. The method of claim 11, whereinchemical treatment agent melts upon contact with the porous particulatesat the second temperature to achieve a viscosity of about 1,000 cps toabout 5,000 cps prior to infusion into the internal interconnectedporosity of the porous particulates.
 13. The method of claim 12, whereinthe plurality of porous particulates comprise porous ceramic proppant.